1. Field of the Invention
The present invention relates to a capacitor in semiconductor device and a method of manufacturing the. More specifically, the present invention relates to a capacitor in semiconductor device and method of manufacturing of the same, wherein an alumina (Al2O3) film capable of further decreasing the effective thickness is used as a dielectric film, instead of a conventional nitride film, and an aluminum (Al) layer is used as a conductive film, thus enhancing the breakdown voltage of the capacitor and decreasing leakage current leading to improved reliability of the device.
2. Description of the Related Art
Recently, the high degree of integration of semiconductor devices has led to a decrease in cell size, and, as a result, it has become more difficult to fabricate a capacitor having sufficient capacitance. Particularly, in dynamic random access memory (DRAM) devices consisting of a MOS transistor and a capacitor, a crucial factor to achieve high integration of DRAM devices is to increase capacitance of the capacitor occupying a large area in a chip while reducing such an area.
In this connection, the capacitor primarily employs poly-silicon as a conductive material, and an oxide film, a nitride film or a lamination film thereof, namely an oxide-nitride-oxide (ONO) film as a dielectric material. Therefore, as methods to increase capacitance (C) of the capacitor, as given by C=(∈0×∈r×A)/T wherein ∈0 represents permittivity of vacuum, ∈r represents a dielectric constant of a dielectric film, A represents the surface area of a capacitor, and T represents the thickness of a dielectric film, there may be exemplified a method involving utilization of a material having a high dielectric constant as a dielectric substance, a method of forming a dielectric film with a low thickness, or a method entailing increasing a surface area of the capacitor.
However, such methods suffer from problems and disadvantages. That is, a great deal of research has been focused on dielectric substances having a high dielectric constant, for example, tantalum oxide (Ta2O5), titanium oxide (TiO2) and strontium titanate (SrTiO3), but it is difficult to apply these materials to practical devices due to the absence of solid confirmation of reliability such as breakdown voltage and thin film characteristics. In addition, decreasing the thickness of the dielectric film results in destruction thereof during operation of the device, this, in turn, significantly affects reliability of the capacitor.
Additionally, a method of increasing a surface area of a lower electrode of the capacitor by forming a poly-silicon layer into multi-layers and then forming the resulting multi-layers into a fin structure connecting each layer therethrough, or a method of increasing a height of the capacitor such as formation of a cylinder-shaped lower electrode on an upper part of a contact suffers from difficulty of subsequent processes due to a step caused by increased height of the capacitor, and high integration of DRAMs leads to a decreased area of the device, thus making it difficult to secure sufficient capacitance of the capacitor.
In addition, since current designs call for twice the number of cells per bit line as in the conventional art, in order to increase cell efficiency, capacitance of the cell capacitor should be further increased, whereas an available surface area of the capacitor is decreased. Therefore, in currently available fin type or cylinder type capacitors, the effective surface area of the capacitor is increased by increasing the height of the capacitor, decreasing the gap between low electrodes, or utilizing hemi-spherical silicon grains.
FIGS. 1a and 1b are views illustrating a capacitor of a semiconductor device in accordance with a conventional art.
First, referring to FIG. 1a, lower structures such as element-isolation oxide films, MOSFET and bit lines are formed on a semiconductor substrate, although they are not shown in FIG. 1a. Next, a lower electrode 12 made of poly-silicon layer pattern is formed on the semiconductor substrate 10 having a contact plug for the lower electrode formed over the entire surface of the resulting lower structures, and an oxide film formed on the surface of the lower electrode 12 is removed by a pre-cleaning process using an HF solution.
Next, a nitride film, as a dielectric film 16, is formed on the surface of the lower electrode 12 via low-pressure chemical vapor deposition (LPCVD) and thermal oxidation is then carried out. As a result, an oxide film 14 made of silicon dioxide (SiO2) is formed between the nitride film 16 and poly-silicon layer 12, and a SiOxNy film 18 is formed on the nitride film 16. Herein, the nitride film 16 can be changed into a SiOxNy material.
Next, referring to FIG. 1b, an upper electrode 20 made of poly-silicon material is formed on the SiOxNy film 18, thereby forming a capacitor having a semiconductor-insulator-semiconductor (SIS) structure.
In such a method of manufacturing a capacitor of a semiconductor device in accordance with a conventional art, the capacitor having the SIS structure is formed wherein the lower electrode 12 and upper electrode 20 are formed of poly-silicon layers, and a nitride film is used as a dielectric film 16. Meanwhile, as a design rule is reduced, the cell area is also decreased, and in order to secure sufficient capacitance, an effective thickness of the dielectric film 16 should be decreased. However, if the effective thickness of the nitride film is reduced to less than 40 Å, oxidation resistance thereof is sharply decreased, which results in problems such as oxidization of lower structures including lower electrode 12 and bit lines during a subsequent thermal oxidation process, increased leakage current of the capacitor itself and attenuation of breakdown voltage.
Further, as the upper/lower electrodes are formed of poly-silicon layers, there are additional problems such as degeneration of electrodes, and formation of oxide films on the dielectric film and electrode interfaces thus increasing the effective thickness of the oxide film and then decreasing capacitance.